Add basic controller specs

- For format.html to make sure instance variable is set
and template is rendered.
- Also add the scenario when the feature flag is not
enabled.
- Update translations

locale/gitlab.pot

@@ -17656,6 +17656,9 @@ msgstr ""
 msgid "Integrations|Note: this integration only works with accounts on GitLab.com (SaaS)."
 msgstr ""
 
+msgid "Integrations|Projects using custom settings"
+msgstr ""
+
 msgid "Integrations|Projects using custom settings will not be affected."
 msgstr ""
 

spec/controllers/admin/integrations_controller_spec.rb

@@ -105,17 +105,44 @@ RSpec.describe Admin::IntegrationsController do
     let_it_be(:overridden_other_integration) { create(:confluence_integration) }
 
     subject do
-      get :overrides, params: { id: instance_integration.class.to_param }, format: :json
+      get :overrides, params: { id: instance_integration.class.to_param }, format: format
     end
 
-    include_context 'JSON response'
+    context 'when format is HTML' do
+      let(:format) { :json }
 
-    it 'returns projects with overrides', :aggregate_failures do
-      subject
+      include_context 'JSON response'
 
-      expect(response).to have_gitlab_http_status(:ok)
-      expect(response).to include_pagination_headers
-      expect(json_response).to contain_exactly(a_hash_including('full_name' => overridden_integration.project.full_name))
+      it 'returns projects with overrides', :aggregate_failures do
+        subject
+
+        expect(response).to have_gitlab_http_status(:ok)
+        expect(response).to include_pagination_headers
+        expect(json_response).to contain_exactly(a_hash_including('full_name' => overridden_integration.project.full_name))
+      end
+    end
+
+    context 'when format is HTML' do
+      let(:format) { :html }
+
+      it 'renders template' do
+        subject
+
+        expect(response).to render_template 'shared/integrations/overrides'
+        expect(assigns(:integration)).to eq(instance_integration)
+      end
+
+      context 'when `instance_level_integration_overrides` is not enabled' do
+        before do
+          stub_feature_flags(instance_level_integration_overrides: false)
+        end
+
+        it 'renders a 404' do
+          subject
+
+          expect(response).to have_gitlab_http_status(:not_found)
+        end
+      end
     end
   end
 end